It is known in the art to cool thermally loaded components in turbo-engines through so-called film cooling. Typical examples may be found in the expansion turbine of a gas turbine engine, where blades, vanes, platforms and other components in the hot gas path, and in particular in the hot gas path of the first expansion turbine stages, are exposed to a hot gas flow with a temperature exceeding the admissible temperature of the materials used for these components, the more when considering the significant mechanical stresses to which the components are exposed when operating the engine.
In applying film cooling, a layer of relatively cooler fluid is provided flowing along the surfaces of the components which are exposed to a hot working fluid flow.
To provide the film cooling fluid on the component surface, ducts are provided in walls of the component opening out on a hot gas exposed surface of hot gas exposed walls of the component. Said ducts are inclined with respect to a normal of the hot gas exposed surface, or hot gas side surface, of the wall. The ducts are in particular inclined into the main direction of the working fluid flowing along the component such as to discharge the film cooling fluid with a velocity component parallel to that of the working fluid, and tangential to the hot gas exposed surface, such that said layer of film cooling fluid is provided. The cooling effect becomes the more uniform the more uniform the distribution of cooling fluid on the hot gas exposed surface is. The distribution becomes more uniform as more holes are used. It is even further improved if slots instead of holes are provided. However, by nature the number of film coolant discharge ducts is limited. On the one hand, the coolant consumption needs to be limited, for instance, in order to avoid compromising negative impacts on the overall engine performance and efficiency. On the other hand, a large number of coolant discharge ducts, in particular if completely penetrating a wall of a component, may compromise structural integrity.
US 2001/0016162 proposes non-penetrating coolant discharge ducts which are in fluid communication with a coolant supply path provided inside the wall. The coolant supply path comprises a near wall cooling duct. In the near wall cooling duct, counterflow convective cooling is effected. Temperature distribution on the hot gas exposed surface of the turbo-engine component thus is rendered more uniform.
U.S. Pat. No. 7,766,618 proposes to provide the coolant discharge ducts as slots with a slot longitudinal direction extending across the main working fluid flow direction. Again, the coolant discharge ducts are shaped as blind cavities and are closed towards a coolant side of the wall. A multitude of coolant discharge ducts join at the hot gas exposed surface in order to provide a common coolant discharge slot with a longitudinal axis oriented across the flow direction of a main working fluid flow. Thus, it is expected to achieve a coolant flow dispersed over the hot gas exposed surface across the main working fluid flow direction. However, as the coolant discharge ducts join immediately adjacent the hot gas exposed surface, still a largely non-uniform coolant distribution on the hot gas side surface is supposed.